Well drilling fluids



tates WELL l)LING.lFLUllDS Clark C. Heritage, Tacoma, Wash, assignor toWeycrhaeuser Timber Company, Tacoma, Wash, 3 corpora- .tion: ofWashington No Drawing. Application August 16, 1951,. Serial No. 242,180

8 Claims. (Cl. 252-85) This invention relates to drillingfluids-employed in rotary Well drilling, and to the use of selectedcomponents and gel strength, inerts such as inert clays which givebodyto the fluid, and chemical conditioning materials for influencing suchproperties as viscosity, filtration rate,

gelling, etc.

The general function of the drilling fluid is to act as a lubricant andcooling medium for the bit and drill stem to remove cuttings anddetritus from the well, and to hold the cuttings in suspension andprevent them from settling when'the circulation of the fluid is stopped.The efliciency with which the drilling fluid performs this function isdetermined by its thixotropic properties, i. e., its ability to thickenupon remaining quiescent and to become fluid upon agitation. Anefficient drilling fluid deposits a thin, impermeable filter cake on thewalls of the hole, thus sealing the walls of the hole and reducing lossof water from the fluid to the formation. The filter cake serves tobridge formation pores and plug smaller openings in'the formation walls,and to prevent caving or sloughing'of' the walls. The weight of thefluid should be suflicientto prevent expulsion by formation liquids, butnot so great as to cause invasion of the drilling fluid into formationsencountered by'the'bit.

The important properties of a drilling mud which are usually tested arethe mud weight or density, viscosity,,.gel strength, filtration rate orWater loss, filter cake thickness, pH, and .mud loss or potential of themud to pass. bodily through the pores of the sand. These properties arelargely physical, but chemical constituents markedly influence thesephysical properties.

The: properties desiredfor well drilling fluids are. determined largelyby the types. and nature of the earth formation 'in which drillingoperationsare being conducted- These properties are obtained byselection. of the kinds of clay most nearly providing theseaproperties,or potentially having such properties which can be developed by thetreatment of the clay with additives and conditioners. It is desiredthat the clay and the combination therewith of additive materials besuchv that the clay can be treated to modify one or more particularproperties, as-nccessitated by changing conditions of drilling, withoutinfecting adversely the stability of other properties.

The instant invention is predicated upon the discovery that certaincomponents of the barks of trees, namely parenchyma tissue, sclerenchymatissue, phelloderm and atent I tures of the same have been usedsuccessfully in the present invention. For convenience in identifyingthem and 2,749,39 Fatented June 5, 1956 cork comprise a group ofmaterials capable of imparting desirable qualities to drilling fluids,and that these may be'used singly or in combination to provide therequired flexibilityof the properties of the fluid. The bark productsdescribed herein, possibly by reason of their chemical reactivity towardother constituents of the drilling fluid, may be used for the purpose ofmodifying the viscosity and weight of the fluid, reducing the pH,decreasing or maintaining the gel time, providing optimum filtrationcharacteristics of the fluid, and enabling the deposit" of a thin, toughfilter cake on the walls of the hole. The use of these bark products asconditioners for well drilling fluids permits desired modifications tobe made in particular properties of the fluid without aflectingadversely other properties required for a satisfactory drilling fluid.

The bark products referred to comprise the cork, and the parenchymatissue and sclerenchyma tissue of the bark phloem. These products may beobtained from the barks of trees, for example the barks 0f theconiferous trees of commerce, bya process which comprises adjusting thefriability of the bark matrix as by controlling its water content, sothat a suitable comminuting process such as ball milling may be employedto pulverize the constituents of the bark differentially whilesimultaneously breaking the bonds therebetween so as to permitseparation of these constituents by selective screening. Processesproviding a combination of comminuting and screening steps, in order toprovide substantially the pure tissue components and certain mixedfractions of the same, are disclosed in Patents No. 2,437,672, issuedMarch 16, 1948, to Herman W. Anway, for Method of Treating Bark; No.2,444,929, issued July 13, 1948, to Raymond S. Hatch, for Method ofTreating Bark; and No. 2,446,551, issued August 10, 1948, to Robert D.Pauley, for Separation of Pure Bark From Finely Comminuted Bark; and.are also disclosed in application Serial No. 572, filed January 5, 1948,by Bror L. Grondal and Calvin L. Dickinson, for Method Of Treating Bark,which application is owned by the assignee of this invention.

As obtained from the above described or similar processes, the phellemor cork fraction is isolated in the'form of particles or flakes of aspongy and resilient character having'a particle size of, for example,plus 28 mesh screen. This product may be obtained substantially freefrom the other components, and is referred to herein simply as Licor .9)

There may also be produced, as a result of the practice of a processsuch as is described above, a product com-. prising essentially bastfibers or stone cells. The bast fibers are usually obtained in the formof elongated fibers having a diameter such as will enable them to passthrough a 65- mesh screen, and having a length of, roughly,tendiameters. Stone cells are characterized by having diametersessentially alike, and may be roughly rounded, polyhedral, shortcylindrical, or very irregular, in general, the stone cells beingwithout particular form. These usually are of a size as to be retainedon a 65 mesh screen.

The parenchyrna tissue as derived from the bark of the Douglas fir, forexample, being readily disintegrated by the action of a ball mill, maybe obtained in the form of apowder of relatively small particle size,for example, a

powder which will pass through a 65 mesh screen. On the other hand, thegreen parenchyma of the Ponderosa pine, known technically as phelloderm,may be obtained in substantially pure form in relatively large particlesizes, the. nature of this product being such that the phelloderm may berecoveredon the largest screens employed in any particular process forseparating the bark contituents.

The above described bark components and various mixreferring to them inconnection with the data and tests subsequently described herein, eachcomponent and mixture used in the tests reported herein is listed belowand given a code designation by which it is referred to herein- It willbe apparent, further, that in a process such as that described above fordifferentially pulverizing bark, and separating the constituents thereofby selective screening, there may also be obtained products comprisingmixtures of said constituents. There may be obtained, for example, aproduct principally comprising from 30% to 90% by weight fiber and to70% by weight cork. This also may be employed in the practice of theinvention.

The percentage composition of the three tissue components of bark variesconsiderably with respect to the barks of different species of trees;with respect to the barks of different trees of the same species,depending on the age of the tree; geographical location, and other suchfactors; and even from different portions of the hole of the same tree.An indication of the variation in content of tissue components of thebarks of different species of trees will be seen from inspection ofTable I, below, showing a percentage analysis of three typical westernconiferous trees, as follows: Douglas fir (Pseudotsuga taxifolia),

western hemlock (Tsuga heterophylla), and white fir (Abies concolor) Theforegoing bark products are compatible with the other materialscustomarily employed in the formulation of drilling fluids. They may beused, for example, in conjunction with most types of bentonitic clays;weighting materials such as barium sulphate, strontium sulphate, ironoxide, pulverized iron, silica flour, etc.; inert clays derived fromvarious sources; chemical conditioning materials including sodiumhydroxide, sodium carbonate, sodium bicarbonate, sodium silicate,tannins, various phosphates, etc., sodium alginate, various gums, andstarch.

The amounts or proportions of bark products to be incorporated in thedrilling fluids are largely variable depending upon such factors as thetype of drilling fluid, the constituents present in the fluid other thanthe bark products, the type of formations encountered during drilling,and others. In general, even relatively small amounts of bark products,e. g. amounts of from .35 pound per barrel of fluid have beensuccessfully employed for imparting desirable properties andcharacteristics to the finished fluid. Substantially larger proportionsof the bark product, as, for example, about 10 pounds per barrel havebeen successfully used. Preferred usages of bark are indicatedhereinafter in connection with the report of specific tests underspecific conditions, but, in general, is about 4 pounds per barrel offluid. Other components, e. g.,

weighting materials, may be present in the same relative proportions inwhich they customarily are used in preparing drilling fluids.

The methods employed in formulating the drilling fluids of the inventionare, generally speaking, those customarily employed in the art for suchoperations. Thus, suitable clays and water may be admixed until thedesired degree of hydration of the clay has taken place. The barkproduct, together with any other desired constituents, is thenincorporated in the mixture and the resulting composition stirred orotherwise agitated as by pumping until all of the components arethoroughly blended together and a substantially uniform mixture isobtained.

Testing procedures and mud characteristics The standard testingprocedure for well drilling fluids is that set forth in API Code No. 29,Second Edition, July 1942, published by the American PetroleumInstitute. The tests reported herein were conducted in accordance withthe API testing procedure, except where otherwise noted. The usual andcustomary tests are mud weight or density, expressed in pounds pergallon (p. p. g.); viscosity, as determined by the Stormer viscosimeter,expressed in centipoises (cps); gel or shear strength, which is measuredinitially and after allowing the mud to set for ten minutes; water lossin cubic centimeters (ccs.) of filtrate in 30 minutes; cake thickness in32nds of an inch; and pH. Water loss and filter cake thickness aretested on the API wall builder equipment.

Density.The general function of mud density, so far as necessity for itscontrol is concerned, is to provide the desired hydrostatic head againstthe formation pressures encountered. The fluid should have a densitysuch that its hydrostatic pressure will be sufiicient to preventdisplacement of the fluid from the well by the pressures encountered inthe earth formations through which the bore passes, but the densityshould not be so great as to cause invasion of the drilling fluid intoformations encountered by the bit. The bark fractions of the presentinvention do not materially affect the mud weights in most instances,and when they do, it is usually to lower the mud weight, due both totheir relative low specific gravity and to a tendency of the bark tofoam in the alkaline mud.

Viscosity.A general objective for viscosity is that it be suflicient toprovide enough body to the fluid to lift the cuttings to the surface,but not so high as to make it diflicult to circulate the fluid throughthe pump and well. There are occasional times when it is necessary toincrease the viscosity, but more often the problem is to lower theviscosity, inasmuch as the colloidal reaction of the clay with waterduring the hydration of the fluid tends to make the fluid viscous.Practically all contaminants, such as cement, salt, anhydrytes and oilalso increase viscosity. Upper limits of a usable viscosity are usuallyabout 200 centipoises Stormer, but it is preferred that the viscosity bemore nearly in the order of 30 centipoises Stormer.

Shear strength.Gel or shear strength is the measure of the thixotropicproperty of the mud; i. e., its ability to thicken upon becomingquiescent and to become fluid upon agitation. An ideal drilling mud isone which is thixotropic, so that upon agitation by pumping or otherwiseit will have a relatively low viscosity and is free flowing, but, whenagitation is stopped, it sets or gels. Its gelling property enables itto suspend the drilling cuttings during cessation or interruption ofdrilling, which would otherwise settle back to the bottom of the hole.Gel is closely associated with viscosity and the same factors whichincrease viscosity will usually increase gel strength, and, vice versa,the factors which lower viscosity will lower gel strength.

Water loss-Water loss is the measure of the degree with which waterseparates from the colloidal suspension by absorption in the earthformation surrounding the well bore. As water loss occurs, the filtercake deposited 15-Min. WaterLoss (cc) -o ir.,-the.walls ofthebore willobviously thicken, because thecake is made up of the residue-of-thedehydrated mud. The dangers from high water loss are (.1) the .filtercake may get-too thick and; the. drill may stick, (2)

water-entering the earth. formation may cause caving and Except for the.fact that a thin, tough filrnof filter cake onv the walls serves toreduce Water loss, it is always desirable to reduce the filter nents,but the parenchyma tissue seemed to provide the greatest. degree. ofwater. loss reduction. .The gel strength on four of the five samples.was already at zero pounds per 100 square feet, and no change wasrecorded by any of the three bark tissues on these four samples. On thefifth sample, the ten minute gel strength was reduced about 20% by eachof the three bark products. Mud weight and cake thickness were notsubstantially affected by any of the products. The pH was loweredslightly in each case, with the parenchyma tissuecausing the greatestchange, the cork tissue the next, and the fiber the least.

TABLE II Water-base mud from Wilmington Field A Rota-Gel mud.

(beutonite) from Wilmington Field Water-base mud, Baroid Chemical, fromRio Vista Field (treated) Water clay oil emulsion type mud fromWilmington Field 508 490' 144 None 508i 110 eso 190 Type of AdditiveBrookfield Viscosity in en Initial Shear Strength in #llOO Sq. FtIOSIVIiIi tShear Strength in #[100 None 140 30-Miu. 'Water'Loss gee.)

fi0-.Min...Water Loss ca)... CakehIhickness in 32nds of an.

inc

cake thickness to the smallset possible value in order toprovid'emaximum clearance for thebit.

pH.-'The hydrogen ion concentration or pH is general not, in and ofitself, critical, except to the extent that it is a measure of changingconditions in the fluid which will affect viscosity, gel strength andwater loss. Control of. the pH may, therefore, be a useful. tool forcontrolling or preventing changes in viscosity, gel strength and waterloss. In general, the clays are alkaline, but no general statements canbe made as to optimum pH. values.

Mud loss .Another characteristic of drilling fluids isthe loss of themud, as an entity, to relatively sound earth formation, and particularlyin the production'zone where the mud penetrates 'the'oil bearing sands.This mud; loss is distignuished from water loss in that in water. lossonly the water passes. .to the formation as a filtrate. In mud loss, theentire mud passes. intov the formation without separation into the waterand clay constituents. Mudloss of this type is also to be distinguishedfrom the mudloss of lost circulation, wherein. the mud exhausts into thelarger pores or cavernous crevises in the earth forma* tion throughwhich the hole progresses. Laboratory experiments and production dataindicate that there is an infiltration of mud into the production: zonewhich remud loss brought about by the use of the bark products of the.present invention.

General efiact of'substantially pure bark tissue compal-rents or:characteristics 0] well drilling muds Oil well drilling fluidsweretreated with substantially pure tissue components. ofbark todetermine-what propertiesof muds, in general, are affected thereby, andto what degree. Five diflerent muds, including one oil-emulsion .typemud, from actual drilling operations, each was treated with 7 pounds perbarrel of each of the three bark tiss-uecomponents, Silvacon 490,Silvacon 508 and Silvacon 1.44. It? was discovered. that. the fibertissue. component .(SilvaconSDS) .wasquite useful. for reducingviscosity in each case, with the viscosity reduction ranging from 14 /2to 43%. In almost all instances water loss was reduced from to by eachof the three bark tissue-compo- I44 Nonei .508 4.90 14.4 700 .490. 880590 None. 508 490 200 120 I44 None 508. 550 390 Inother tests comparisonwas made between substantially pure parenchyma tissue and fiber-intheireffects on treatment of water-base'drilling mud, when used togetherwith caustic soda in the ratio of four parts bark to one part caustic,by weight; These results are shown in Table V hereof, columns B, C, andE, F, under the section on Treatment of water-base muds. It will beobserved, by reference to Table V, however, that the fiber reducedviscosity to a considerably greater extent than parenchyma tissue, butparenchyma tissue was more effective in reducmg water loss. Tests haveshown that the fiber is effective for reducing viscosity of the drillingfluid when used in amounts as small as .35 lb. per barrel of fluid. Apractical upper limit for this purpose may be set at 10 lbs. per barrel.

Treatment of water base muds It has been found that best results in thetreatment of water base muds is had by the use of bark products andcaustic soda in a ratio of about 4 parts of bark to 1 part of causticsoda, by weight, with the bark at usages of about fl pounds per. barrelof drilling mud. For the data shown in. Table III, below, a mudrepresentative of a typical hole-made mud was prepared by mixingapproximately 1 part of bentonite, 2 parts Dixie clay (a very slightlyhydratab'le, kaolin type of clay) and 14 parts water. The bentonite wasadded in the form of a completely hydrated slurry. The mud had a solidscontent of about 19%. The characteristics of the mud before treatmentareshown in column A of Table III. The bark and caustic used as treatingagents were added in a slurry containing 20 pounds of water per barrelfor each'4 pounds of bark per barrel.

Severaltests were run in order to determine to-what extent eachingredient in the Silvacon-caustic treating slurries alfected the finalresults. From the data obtained from these tests it appears that. wateralone causes a viscosity reduction and a. slight increase of water loss.Caustic, without Silvacon, causes extreme flocculation withcorresponding increases in viscosity .and water loss. Silvacon 218,without caustic, causes excellentviscosity reduction, but only a slightdecrease in water loss. A treating agent made up of: Silvacon 218' andcausticsoda in a ratio of 4 to 1 showed excellent water loss' andviscosity reducing; properties.

TABLE HI water-base mud Column A B O D Bark, p. p. b 4 1 4 Caustic, p.p. b 0 0 25 1 TESTS IMMEDIATELY UPON MIXING Weight, p. p. b 9. 36 9. 339. 30 8.81 Viscosity (Stormer, c 110 38 28 37 Initial Gel Strength 11m)-130 12 4 5 min. gel strength. 140 25 7 8 Water loss (cc. 30 in.) 22 21.7 18 14. 4 Cake thicknessQz' 7 5 4 4 H .9 10.8

8.33 y 34 Initial gel strength. 5 10 min. gel strength... 160 16 6 Waterloss 22. 1 21. 7 17.8 15. 5 Cake thickness... 5 4 4 pH 6.4 5.3 7.9 9. 9

It will be observed from Tables III and IV that marked improvement wasobtained in viscosity, shear strength and cake thickness by the use ofbark alone without caustic soda; that the greatest reduction inviscos1ty was obtained by the smallest usage of bark as shown in columnC of Table III; and that a reduction of water loss of about 20% or morewas obtained using bark and caustic in the ratio of 4 parts bark to 1caustic.

Table IV is an extension of the tests conducted in In" Table V, below, aseries of tests were rim to determine the relative eifects of other barktissue components and the preferred bark product of 10% cork, 40% fiberand 50% parenchyma tissue (Silvacon 218). The mud was a high viscosity,high water loss mud quite similar to that used in Tables III and IV. Itconsisted of 1 part by weight of bentonite, 2% parts of Dixie clay, and18 parts water. The API characteristics of this mud are given in columnA in Table V. The bark and caustic were added in a slurry containing 20parts of water. Slurries were prepared of the following bark products:

. 4 parts Silvacon 218 4 parts Silvacon 508 4 parts Silvacon 490 4 parts50% Silvacon 490 and 50% Silvacon 508 4 parts 65% Silvacon 490 andSilvacon 508 4 parts 70% Silvacon 412 and 30% Silvacon 490 4 partsSilvacon 412 The results of tests are shown in the following table. Itappears that a blend of 65 Silvacon 490 and 35% Silvacon 508 producesresults very similar to those produced by Silvacon 218. By and ofitself, Silvacon 490 is more chemically active than Silvacon 218, asshown by lower pH and water loss values. Conversely, Silvacon 508 isless active than Silvacon 218, as shown by higher pH, lO-minute shearand water loss values. The blend of 65 parenchyma tissue and 35 fiber issubstantially as active as the Silvacon 218 blend of 10% cork, fiber andparenchyma tissue.

TABLE V Effect of diflerent bark products on high viscosity, high waterloss, water-base mud BARK AND CAUSTIC ADDEDPll'gN A SLURRY CONTAINING 20P. P. B. OF WATER R 4 P. P. B. BARK Column A B C D E F G H I BarkProduct o e 508 490 21s gig; 508 490 21s 21s Bark, p. p. b 0 4 4 4 4 2 22 1 Caustic, p. p. b 0 1 1 1 1 5 5 5 .25

TESTS IMMEDIATELY UPON MIXING Weight 9. 25 8. 72 8. 37 8. 78Viscosity... 84 85 47 38 38 35 47 45 30 Initial gel strength- 85 6 5 5 55 6 5 6 10 min. gel strength 115 25 10 8 8 30 22 20 18 30 min. Waterloss (00.) 18. 3 15. 1 10. 8 12. 5 12. 7 15. 3 l3. 2 13. 6 15. 7 Cakethickness (l2) 5 4 3 3 3 4 4 4 TABLE IV Eflct of variation in usages ofSilvacon 218 on viscosity and water loss of mud in Table III TESTSIMMEDIATELY UPON MIXING .Oolumn A B C D E F G -Bark, p. p. b" 0 1 2 3 44 O Caustic, p. p 0 2E- 5 -76 1 O 1 3 Viscosity 110 28 29 36 37 38 V. F.Water 1085. 22 18 17. 5 16. 2 14. 4 21. 7 23. l

V. F.--Very flocculated; so viscous, not measurable.

In Table VI comparisons were made between bark products identified asSilvacon 218, Silvacon 412, and Silvacon 383, the latter consistingpredominately of cork and being micropulverized through a 0.027 screen.The composition of the mud was as follows: 1 part by weight of bentoniteadded in the form of a well-hydrated slurry, 3.2 parts of anonhydratable kaolin type clay consisting of a blend of 1 part Dixieclay and 4 parts china clay; and 17.3 parts of water. The API testcharacteristics of the untreated mud are shown in Column A of Tavle VI.The mud was then treated with bark products and caustic in amounts offrom 2 to 4 pounds of bark and .5 to 1 pound of caustic per barrel ofdrilling fluid (a ratio ofapproximately 4 parts bark to 1 part caustic),as shown in the table. The bark was added to the mud in dry form and thecaustic was added as a 50% solution.

ai ments TABLE VI Efiect of difierent bark products on high viscosity,high water loss, water-base mud of whole mud are-lost to the formationbefore a mud cake is. formed. This intrusion of solid particles intothepore .channelsofa producing formation will reduce or even stop theflow of. oil. through these channels when a well is put. on production.It will be recognized Column A B D 11 F G H 383M 218 412 218 41 2 383M 23 a 4 4 4 .5 .75- .6 1- '.8 1 9.45 9. 44 0.411 9.44 9.44 9.44

50 a1 41 4s 32 41 5 6 6 5- 5 6 24 s 31 s 25 1 13.7 13.2 13.8 13.0 13.913:5

The improved results of treatment of water-base muds ment is not so muchrelated to the well drilling" fluid with bark mixture 218 noted inlaboratory tests were concharacteristics in its etfect upon .the conductof the'drilling firmed in a number of actual drilling operations- Obseroperation as it'is in connection with the improvement 'in vations madeduring actual drilling operation have shown the yield of oil from thewell. The only difierence. so that the bark should be added to the mudfirst, followed far as the well drilling operation is concerned is thatby the caustic, and that each ingredient should be added the consumptionof mud used is reduced. This is in during one cycle of circulation. Thebark can be added and of itself an important improvement as it reduces.the dry, but it is recommended that the caustic soda be added cost ofdrilling. However, it should be understood. that .in solution form at asteady rate. the improvement in API characteristics of the mud, and Thebark reduces the gel requirement for the mud bereductions of' mud loss,may, and do, probably, in most cause of the capacity of bark-treatedmuds to be thinned instances, occur simultaneously. The success ofbark'as with water without marked increase in water loss. This, apore-bridging; material can probably be attributed'to the in turn,eliminates theneed for viscosity reducing agents. combined functions itperforms in a drilling mud, i. e;, This property of the bark results, atleast in part, from chemical dispersion and mechanical bridging. thepresence of the. hast fibers which mechanically reduce A typicalwater-base mud was prepared and tested for water 'loss and are notchemically consumed in the treatmud-loss using four different'sands. Themud was made ment, nor affected by dilution of the mud with water in bymixing 10% of" a bentonite clay mud having 7% limited amounts. solidscontent and 90% of a Rogers Lake: 1 -34 mud (native-type clay) having36% solids content. Water Pwebndgmg or mud loss prevenrtmn was added'so" that the mud, when ready for testing; con- The loss of mud referredto is a gradual loss to sound 'in d about 21.5% lid A i emulsionmud, comearth formations, and is to be distinguished from the loss id d t b t ial, was prepamd b ddi th water of mud generally referred to as lostcirculation." This base mud thus prepared a Wilmington Field crude oilloss is particularly objectionable in the oil production in. an31119311133116}! th t h fi l d ready f in zone where the mud penetratesthe oil bearingsand and m 'i azo z, b l f il; the flow of'o'il to thehole is substantially retarded, Un- 0 Q sample f h d was tested wi htreat. 165$ p p y" treated, Whole mud will flow gh the merit;anothersample was treated with four "pounds per P channels until the P pSize Solid Particles PP barrel of quebracho; and another sample wastreatedwith along to bridge the openings. 'Thus, appreciable a u s fourpounds per barrel of bark product, Silvacon 21'8,

consisting approximately of 10% cork, 40% fiber and parenehyma .tissue.Tests were conducted. immediately after mixing of the muds and thetreating agents. Standard API test values and mud loss values determinedon both the treated and untreated Water-base and oilthat the. natureofthis. improve- 5 emulsion mud's are set forth in Table VII, below:

TABLE Comparison of pore-bridging effects of bark and quebracho withthreadifier ent filter media sands and two difier'ent drilling fluidsTests M... Typieal'Water Base Mud Typical Ofl Emulsion. Mud

Treating "Agent None Quebracho gfg Quebmcho gi Usage. None 4 p. p. b. 4p. p. b. 7 None 4 p. p. b. 4 p. p. b.

Welghtuse a as s. 41 s. as 8.52 9.03 Viscosity 14 18 16 28 35 25 Initialgel-strengthen. 5" 5. 4 5' 9 5 10 min. gel Strength 20 30. 20 20 45 25vWaterLoss. 14.2 13 12:7 8. 8 6; 3' '7. 2 Cake Thlclm 3 2. 3" 3 2 2 pH.9. 3 8.2 8.3 9. 3 8.2 8.2

MUD LOSS-SAND BLAST "SAND (MEDIUM SAND-96 DARCYS) r 11 TABLEVIl.-Continued MUD LOSS-DEL RAY SAND #20 (MEDIUM SAND-116 DARCYS) TestsTypical Water Base Mud Typical Oil Emulsion Mud Treating Agent NoneQuebraeho gfg Quebraeho gfg Usage None 4 p. p. b. 4 p. p. b. None 4 p.p. b. 4 p. p. b

app]

When a medium sand having a porosity of 96 darcys was employed, aconspicuous difference in mud loss was noted in both the typicalwater-base mud and the oilemulsion mud. Only the bark treated sampleswere sufliciently impermeable to the filter medium to prevent mud loss.As the sand increased in coarseness to 116 darcys in the Del Ray sandand 156 darcys in the Monterey sand, the permeating potential of themuds to the sand filter was even more conspicuously differentiated. Itwill be seen that the mark treatment greatly reduces the propensity ofthe mud to pass through the pores of the sand filter, whereas thequebracho provides little more retarding effect than the untreated mud.

Other tests were made with drilling muds of diflerent compositions andusing 2 and 5 pounds per barrel of the following treating agents:Silvacon 218; Silvacon 412; Silvacon 412G; Silvacon 490; quebracho; andsodium tetraphosphate, known to the trade and referred to hereinafter asQuadrofos. The results are shown in the following table:

TABLE VIII Comparison of pore-bridging eflects of different barkproducts and difierent usages Mud Loss in cc. Line Bark Product Finenessi gf Min. 80 Min.

A"--. None 0 60 'Sample through in 15 sec. B-.-" Silvacon 218. 65 2 2256. C do 65 5 14 36. D..- Silvacon 412... 28 +65 '2 50 118. E do -28 +655 70 F..-.- Silvacon 412G- 65 +325 2 38 81. G do 65 +325 5 25 57.

H..... Silvacon 490... 325 2 40 108. I do 325 5 i3 64. J Quebracho.-.. g2 62 Sample through K.. Quadrofos in sec.

Where excessive mud loss was encountered, the drilling fluid was treatedwith two pounds per barrel of a I bark mixture of approximately cork and75% fiber (Silvacon 412), of which half the quantity was its normalparticle size as produced at the bark plant (-28 +65 mesh) and the otherhalf was ----65 +325 mesh size (Silvacon 412G). Mud loss at the welldropped from 25 barrels per hour to a negligible figure. API testcharac- Q teristics were either improved or not materially affected.

2 Tests on the mud before and after treatment at the well, .using amodified mud loss testing procedure in which well.

1 lfinire sample spurted through the filter in the time within which thepressure was the sample is passed through a 2 centimeter column of sandhaving a porosity value of 494 darcys water permeability, were asfollows:

TABLE IX Effect on mud loss and other properties of well drilling fluidin actual operation by addition of 2 p. p. b. bark mixture Contaminatedmuds The bark tissue components of the present invention have been foundto be especially useful for reconditioning contaminated drilling muds,either water base or of the oil-emulsion type. The bark ingredient maybe added after the mud has been contaminated, in which case itsbeneficial effects are referred to as corrective action, or it may beadded before the mud becomes contaminated in anticipation of such event,in which case the beneficial effects of the bark are referred to aspreventative action.

The contaminants commonly encountered in oil well drilling operationsare salt, anhydn'tes such as calcium sulfate, and cement. These causethe drilling fluid to become highly flocculated, with a separation ofsolids and water and a consequent increase of viscosity and loss ofwater to the earth formation. The troublesome element in cementcontamination is calcium hydroxide or lime. The calcium ion flocculatesthe clays in the mud, causing the solids to coagulate and the water topull away. The condition is known to practically every Silvacon 218 hasa marked defiocculating effect on a cement contaminated drilling mud,but is not effective when used alone as a treating agent for saltcontaminated mud. The addition to bark products of an alkali such assoda ash or caustic soda creates a combined chemical and mechanicalaction and resuspends the clays. In tests showing use of mark productsas treating agents,

' the untreated mud samples spurted through the filter,

leaving mud infiltrated sand. Bark treated mud lays a.

area-son thin brown layer /s") on the surface of the sand, and allsolids and of the water remain in themud.

Tests were conductedadding varying usages of bark products, Silvacon 218and Silvacon 412, to a cementcontaminated, water base, highbentonite-content drilling mud. The results of this work, asrecapitulated in Table X, clearly show the excellent defloccul'ating andconditioning efi'ect of treating the mud with bark products.

TABLE X The alkali is added and is stirred into the mud by the action ofthe pump in circulating the mud through the system. The alkali should bedissolved in water in the chemical barrel and run into the mud at asteady rate. Concentration of the alkali is flexible and canbe adjustedto almost any convenient figure, as long as the ratio of solid causticto bark product is maintained in the neighborhood of 1 to 4. Prior todrilling out cement, the bark The efiect of Silvacon 218 and Silitacon412 an cement contaminated, bentam'te drilling mud xiiiii D r 30 in CakeCement Sllvac'on, Stormer m egree? m Thick- W- e an. are 1:22

0 0 20- -45 None 12.4 s- 8.10 8.63 0' 4-218 3-35. None 12.2 aaae 0.0 1 054 110-230 F 14.0 5+- 8.70 11.0 1 4-218 24 7. a5 Ntme 12.5 a 8.12 9. 412 0 VF VF VF 15.0 0- VF 11.8 2 4-213 8-45 None 13. 2 a s; as 10. 3s 34-218 43 43-120 F 14. 4 5 8. 44 11. 12 2 5-412 31+ 20-70 SF 13.5 3- am 710.87

F=tloeculated.

Bark products, used in conjunction with alkali, are efiective treatingagents for salt contaminated muds. Salt isa commonly encounteredcontaminant in oil well drilling, and has a very decided efi'ect on theproperties of normal water base muds. Primarily, the effect is to breakthe gel system, and the consequent fiocculated muds show highviscosities, shear strengths and water losses. It salt contaminationruns over 1%, it is usually cheaper to discard the mud and substitutespecial salt. tolerant mud systems. Even salt contaminations of lessthan 1% are expensive to treat and provide a most. rigid test for theefliciency of a treating material.

In the treatment of salt contaminated muds,. an alkali, usually causticsoda, is added to raise the pH of the mud to 11.5 or above. The barkproduct usage is in amounts of 3, 6, 9', 12 and 15 pounds per barrel.For purposes of the tests reported in the following table, the clay wasmade into mud by using a 12% brine. The results indicate that a.reduction in water loss of any salt contaminated mud is possible bymeans of treatment withabark product. The use of bark lowers the highsalt induced viscosities and reduces water losses, even in highercontaminated salt muds. The following table shows the effect of barkproducts as treating agents for a salt contaminated drilling mud.

TABLE XI contaminated mud. 12% contamination product should be added tothe mud as is, and the-addition of caustic should be discontinued.

below, showthe useful improvement which. is. to be obtained when a barkproduct and another treating agent are used in combination; and that thecombination generally produces better results than either barkor theother treating agent alone. This knowledge is particularly useful asshowing the compatibility of the bark with other treating agents, for itmay'we'll be that another treating agent will have been used in the mudprior to the time that it becomes contaminated with cement. It may alsobe desirable in certain instances to add both bark and another treatingagent where the other treating agent has been found to be efiicacious inproviding a particular characteristic to the drilling fluid. The mud inthe tests reported in Table XII was a water base mud made up ofi amixture of six parts of a 31% solids,Rogers Lake P-34 mud, and

one part of a 7% solids, bentonite mud. This mud was then contaminatedwith 2 pounds per barrel of ordinary Portland cement added in the formof a water slurry. The bark and other treating agents were added dry.Tetrasodium pyrophosphate (TSPP) and sodium bicarbonate The bark productmay be added dry, either directly into the pit or through the hopper,and is distributed evenly throughout the mud by the action of the pumpin circulating the mud through the system.

were selected as representative of other treating agents. As betweenbark and the said other treating agents tested, bark was much superiorin water loss and viscosity reduction as will be seen in columns B, C,and F.

15 TABLEXII' E'fiect of bark product, tetrasodium pyrophosphate, and

sodium bicarbonate, as treating agents for cementcontaminated,water-base drilling muds Column A B O D E F G 61 9. 90 Viscosity VF 2434 25 27 25 73 Initial gel strength 250 4 4 5 ll 4 10 min. gel Strength350 50 60 40 30 140 Water lOSS 19. 5 13. 9 15. 7 13. 3 13. 0 16. 8 l2. 7Cake thickness 10 5 6 4 4 6 4 pH 12. 3 11. 6 12. 5 11. 4 11. 6 12. 1 11.4

VF-very flocculated, too viscous to measure.

Having described my invention and how the same may be used, what I claimas new and desire to protect by Letters Patent is:

1. An aqueous drilling mud made up of a major proportion of a suspensionof water insoluble clayey material in water and an amount of a mixtureof an alkali metal hydroxide and a separated component of the bark of aconiferous tree of the pine, tsuga, pseudotsuga and fir familiesselected from the group consisting of sclerenchyma tissue,

parenchyma tissue, cork and admixtures thereof, the bark component beingpresent in the range of from 0.35 pound to about 10 pounds per barrel offluid.

2. The aqueous drilling mud of claim 1 in which the clayey material isMojave clay and the alkali metal hydroxide is sodium hydroxide.

3. The aqueous drilling mud of claim 1 in which the clayey material isbentonite clay and the alkali metal hydroxide is sodium hydroxide.

4. The aqueous drilling mud of claim 1 in which the clayey material isMcKittrick clay and the alkali metal hydroxide is sodium hydroxide.

5. A drilling mud comprising an aqueous suspension of a clayey materialin water and from about 0.5 to 4.0 pounds of a mixture of an alkalimetal hydroxide and a separated component of the bark of a coniferoustree of the pine, tsuga, pseudotsuga and fir families selected from thegroup consisting of sclerenchyma tissue, parenchyma tissue, cork andadmixtures thereof, per barrel of mud, the proportion of the said barkcomponent to fluid being in the range of from 0.35 pound per barrel toabout 10 pounds per barrel.

6. A well drilling fluid comprising a clayey material, water, aseparated component of the bark of a coniferous tree of the pine, tsuga,pseudotsuga and fir families selected from the group consisting ofsclerenchyma tissue,

459 and 461.

parenchyma tissue, cork and admixtures thereof, the said bark componentbeing present'in an amount in the range of from 0.35 of apound to about10 pounds per barrel of fluid, and caustic soda in the proportion ofabout 1 part to 4 parts of the bark product.

7. A well drilling mud comprising an aqueous fluid mixture of hydratedclay in water, a comminuted bark product derived from the bark of aconiferous tree of the pine, tsuga, pseudotsuga and fir familiesconsisting of approximately 10% cork, 40% fiber and 50% parenchymatissue, and caustic soda in the proportion of about 1 part to 4 parts ofbark fraction the proportion of the bark product to fluid beingin therange of from 0.35 pound per barrel to about 10 pounds per barrel.

8. A well drilling fluid comprising a clayey material, water, aseparated component of the bark of a coniferous tree of the pine, tsuga,pseudotsuga and fir families selected from the group consisting ofsclerenchyma tissue, parenchyma tissue, cork and admixtures thereof, andcaustic soda in the proportion of about 1 part to 4 parts of bark theproportion of the bark product to fluid being in the range of from 0.35pound per barrel to about 10 pounds per barrel.

References Cited in the file of this patent UNITED STATES PATENTS1,999,766 Lawton et al. Apr. 30, 1935 2,109,858 Cannon Mar. 1, 19382,280,995 Booth Apr. 28, 1942 2,549,142 Thompson Apr. 17, 1951 2,601,050Nestle June 17, 1952 FOREIGN PATENTS 605,173 Great Britain of 1948 OTHERREFERENCES Langton: Fibrous Materials Aid Restoring Lost Drilling WellCirculation, Article in The Oil and Gas Journal, April 23, 1936.

Stem: Role of Clay and Other Minerals in Oil Well Drilling Fluids,Bureau of Mines Report of Investigations No. 3556. February 1941, pp. 67and 68. (Copy in Div. 64.)

Weyerhaeuser Oil Well Drilling Products, Forms 911, 912, 913, and 914,also pamphlet on Improved Silvacel Fiber, 20 pages total printed matter,1950.

Allen: Commercial Organic Analysis, vol. III, P. Blakistons Son and Co.,Philadelphia, Pa. (1900), page 23.

Rogers: Composition and Properties of Oil Well Drilling Fluids, GulfPub. Co., Houston, Texas (1948), pages

1. AN AQUEOUS DRILLING MUD MADE OF UP A MAJOR PROPORTION OF A SUSPENSIONOF WATER INSOLUBLE CLAYEY MATERIAL IN WATER AND AN AMOUNT OF A MIXTUREOF AN ALKALI METAL HYDROXIDE AND A SEPARATED COMPONENT OF THE BARK OF ACONIFFEROUS TREE OF THE PINE, TSUGA, PSEUDOTSUGA AND FIR FAMILIESSELECTED FROM THE GROUP CONSISTING OF SCLERENCHYMA TISSUE, PARENCHYMATISSUE, CORK AND ADMIXTURES THEREOF, THE BARK COMPONENT BEING PRESENT INTHE RANGE OF FROM 0.35 POUND TO ABOUT 10 POUNDS PER BARREL OF FLUID.